Organometallics 1987, 6, 868-872
868
Ion Pairing of [Fe3(p-H,p-CO)(CO),,,]-
with H,NR2+ Cations
C. K. Chen, C. H. Cheng," and T. H. Hseu' Department of Chemistty and The Institute of Life Science, National Tsing Hua University, Hsinchu, Taiwan 300, Republic of China Received August 14, 1986
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The bridging vCoof [H2R2N]+[HFe3(CO),,](R = Et, n-Bu) appears at 1550 cm-I in the solid state, at 1650 cm-' in benzene or chloroform, and at 1745 cm-' in THF'. The corresponding vco of the H2(i-Pr)2N+ salt also occurs at about the same position as that of the H2R2N+salt in the same solvent. In the solid state, however, in addition to a new band at 1883 cm-' in the terminal CO region the bridging vco appears at 1650 cm-'. There is no similar terminal band in the other salts. The crystal structure of [H,(iPr),N] [HFe,(CO),,] was determined by a single-crystaldiffraction method. The structure details indicate that the bridging CO group and one of the terminal CO groups are each hydrogen-bonded to an acidic proton on two separate cations. The hydrogen bonding provides a basis for the understanding of the vco change of HFe3(CO)''- with its environment. The bridging vco at 1740,1650, and 1550 cm-' is explained as the consequence of the formation of none, one, and two hydrogen bonds, respectively, between the bridging CO and the countercations.
Introduction Ion pairing of metal carbonylates with their countercations has attracted considerable interests in recent years. The results of the studies have shown that the coordination of alkali ions to the carbonyl oxygens greatly accelerate the alkyl migration in RFe(C0)4-1-3and increase the reactivity of HFe(CO), toward oxygen m ~ l e c u l e . On ~ the other hand, the hydrogen bonding between the bridging CO of HFe3(CO)11-and "Et3+ reduces the CO scrambling rate in the carbonyl anion.5 While extensive studies on the ion pairing of mononuclear metal carbonylates have been c ~ n d u c t e d , ' - there ~*~ is much less work concerning the same phenomena in cluster^.^^^*^ Our interests in the ion pairing of metal cluster anions have been focused on the interaction of HFe3(CO)11-with its countercations and with solvents. The cluster anion has a single bridging CO group that in most cases is the center for ion pairing and solvation. The IR absorption frequency of this CO group appears in a region that is not interfered by most solvent absorptions and by terminal CO absorptions. These unique features enable us to look into the details of the interactions of the iron carbonylate with its environment by measuring the CO frequency change. In a previous paper: we had shown that MHFe3(CO)11(M = alkali metal) exists as ion pairs in the solid state and in ether and dioxane, but the salts dissociate partially in T H F solution and both contact ion pairs and less associated forms are present. In more polar solvents, the alkali salts exist only as less associated forms. However, the interaction between the bridging CO and the acidic protons on the solvent molecules becomes important. A recent study on the ion pairing of HFe,(CO),,- and the analogous HRu3(CO)1; with PPN' and NEt4+showed that (1) Collman, J. P.; Finke, R. G.; Cawse, J. N.; Branman, J. I. J. Am. Chem. SOC.1978, 100,4766. (2) Mclain, S.J. J. Am. Chem. SOC. 1983, 105, 6355. (3) (a) Powell, J.; Gregg, M.; Kuksis, A.; Meindl, P. J.Am. Chem. SOC. 1983, 205, 1064. (b) Powell, J.; Kuksis, A.; May, C. J.; Nyburg, S. C.; Smith, S. J. J. Am. Chem. SOC. 1981, 103, 5941. (4) Darensbourg, M.; Barros, H.; Borman, C. J. Am. Chem. SOC. 1977, 99,1647. (5) Wilkinson, J.; Todd, L. J. J. Organomet. Chem. 1976, 118, 199. (6) Kao, S.C.; Darensbourg, M. Y.; Schenk, W. Organometallics 1984,
3, 871.
(7) Collman, J. P.; Finke, R. G.; Matlock, P. L.; Wahren, R.; Komoto, R. G.; Brauman, J. I. J. Am. Chem. SOC.1978, 100, 1119. ( 8 ) Chen, C. K.; Cheng, C. H. Inorg. Chem. 1983,22, 3378.
these salts in solutions form contact ion pairs and less associated species that may be distinguished from each other in the IR ~ p e c t r a . ~A brief investigation on the interaction of "Et3+ with HFe3(CO)11-also had been reported previ~usly.~ In this paper, we wish to present some novel examples of the ion pairing of metal carbonylates in the solid state and solutions that exhibit dramatic change in the CO frequencies with the environment. The systems investigated are several of the dialkylammonium salts of the HFe3(CO)11anion. Moreover, the X-ray structure determination of one of the salts is also reported. The results give direct evidence for the contact ion pairing of the HFe3(CO)1; anion with its countercation in the solid state. Although the ion pairing of a large number of metal anions has been investigated, there are only a few mononuclear that provide crystal structure evidence for such behavior. The present structure is believed to be the first example describing the interaction of a cation and metal carbonyl cluster anion in the crystalline state.
Experimental Section All experiments were carried out under an atmosphere of nitrogen by using modified Schlenk techniques. IR spectra were recorded on a Jasco 100 spectrophotometer. Iron pentacarbonyl (Strem) was used as purchased, while KHFe3(CO)" was prepared according to the method reported
previously by US.^ H2Et2N+C1-,H2(n-Bu)2N+Cl-,and H2(iPr)2N+C1-were obtained by the addition of a stoichiometric amount of hydrochloric acid to the corresponding dialkylamine in methanol followed by evaporation of the solution. Preparation of Dialkylarnmoniurn triangulo -(bCarbonyl)decacarbonyl(M-hydrido)triferrate( 1-), [H,R,N][HFe,(CO),,]. To 1.00 g of KHFe3(CO)'' in 10 mL of water was added 1.1 equiv of dialkylammonium chloride in a
(9) Schick, K.-P.; Jones, N. L.; Sekula, P.; Boag, N. M.; Labinger, J. A.; Kaesz, H. D. Inorg. Chem. 1984,23, 2204. (10)Chin, H. B.; Bau, R. J. Am. Chem. SOC.1976, 98,2434. (11) Teller, R. G.;Finke, R. G.; Collman, J. P.; Chin, H. B.; Bau, R. J. Am. Chem. SOC.1977, 99,1104. (12) Calderazzo, F.;Fachinetti, G.; Marchetti, F. J. Chem. SOC., Chem. Commun. 1981, 181. (13) Fachinetti, G. F.;Floriani, C.; Zanazzi, P. F.; Zanzari, A.R. Inorg. Chem. 1978, 17,3002. (14) Schlussler, D. P.;Robinson, W. R.; Edgell, W. F. Inorg. Chem. 1974, 13, 153.
0276-7333/87/2306-0868$01.50/0 0 1987 American Chemical Society
Ion Pairing of [Fe3(p-H,p-CO)(CO),J -
Organometallics, Vol. 6, No. 4, 1987 869
Table I. Fractional Coordinates (XlO') for t h e Non-Hydrogen Atoms of [H,(i-Pr),N][HFe,(C0),,1 atom
xla 2117 (2) 293 (1) -81 (2) 3723 (17) 2132 (11) 1749 (15) 2894 (13) 876 (14) -195 (12) -1410 (13) -827 (16) 19 (13) 1008 (14) -1777 (15) 4813 (11) 2998 (9) 1631 (13) 3531 (11) 1323 (12) -485 (11) -2467 (10) -1426 (12) -7 (14) 1634 (11) -2779 (12) 4477 (9) 4511 (13) 5110 (19) 2962 (16) 5869 (12) 5643 (19) 6481 (16)
Ylb 1301 (1) 627 iij 1895 (1) 885 (7) 905 (6) 1458 (7) 2032 (6) -145 (6) 641 (7) 455 (6) 1714 (8) 2696 (6) 1982 (7) 1876 (7) 614 (6) 844 (4) 1509 (6) 2491 (5) -660 (5) 633 (5) 309 (6) 1673 (6) 3214 (5) 2056 (5) 1886 ( 8 ) 1322 (5) 792 (6) 1071 (8) 654 (9) 1531 (8) 2142 (10) 988 (10)
ZIC
-3666 (1) -2925 iij -3066 (1) -3654 (11) -2177 (9) -5236 (12) -3182 (10) -2820 (11) -1576 (10) -3937 (12) -4561 (12) -3397 (10) -1573 (11) -2704 (13) -3534 (11) -1258 (7) -6191 (8) -2868 (8) -2715 (9) -693 (8) -4544 (9) -5521 (8) -3661 (9) -646 (7) -2449 (11) 970 (7) 1865 (11) 3068 (11) 1687 (12) 766 (11) 72 (15) 165 (15)
minimum amount of water. The precipitate was filtered, washed by distilled water, and then dried in vacuo t o give the desired product. T h e presence of HFe3(CO),< in these salts were identified by comparing their CO stretching frequencies and the chemical shift of the hydride (6 -14.94 in MezSO-ds) with the corresponding data of the known (HNEt,)[HFe3(CO)11], while the existence of the dialkylammonium cations was confirmed by the 'H NMR spectra of these complexes in MezSO-d,. S t r u c t u r e Determination of [Hz(i-Pr),N][ HFe3(CO),,]. Crystals suitable for crystallographic measurements were obtained from benzene-hexane mixture. The compound crystallizes in the monoclinic space group P2,/c with a = 9.635 (4) A, b = 21.182 (7) A, c = 11.897 (5) A, and @ = 104.01 (3)O. The density calculated for four molecules per unit cell is 1.632 g ~ m - ~All. crystallographic measurements were made on a Nonius CAD-4F automatic diffractometer with Zr-filtered Mo K a radiation (A = 0.71069 A). Intensity data were collected at room temperature with use of a 8-20 scan technique. The intensities of three standard reflections were remeasured periodically and were used to rescale all the data by use of a linear interpolation procedure. Intensity data from azimuthal rotation about the two strong reflections 200 and 080 were used for the absorption c ~ r r e c t i o n '(fi ~ = 19.3 cm-'). Of a total of 5583 independent reflections with those 20 < 55' ((sin O)/A 5 0.65) collected, 2956 were found to have intensities greater than 3 times their estimated standard deviations. Only these reflections were used in the subsequent analysis. The structure was solved by the heavy-atom method and refined by the full-matrix least-squares method. The function minimized was xlu(lFol - lFc1)2with the weighing scheme given by Stout and Jensen.16 The atomic scattering factors used were all taken from ref 17, with that of Fe corrected for anomalous dispersion. Except the bridging H atom, the positions of the hydrogen atoms were calculated with C-H = 0.95 A, N-H = 0.9 A, and a tetrahedral
(15) North, A. C. T.; Philips, D. C.; Mathews, F. S. Acta Crystallogr., Sect. A: Cryst. Phys., Diffr. Theor. Gen. Crystallogr. 1968, A24, 351. (16) Stout, G. H.; Jensen, L. X-ray Structure Determination; Macmillan: New York, 1968, P 457. (17) International Table for X-ray Crystallography; Kynoch Press: Birmingham, 1962; Vol. 111, pp 201-203.
F i g u r e 1. A perspective view of the structure of the anion in [H2(i-Pr),N1 [HFe3(CO),,-I.
Figure 2. Crystal packing diagram of [H2(i-Pr)2Nl[HFe3(CO),,I viewed along the b axis (hydrogen bonds are indicated by dashed lines). angle of 109.50'. The positional and isotropic thermal parameters of all H atoms were included in the calculation but not refined. The final refinement with anisotropic thermal parameter for non-hydrogen atoms led to values of R and R, of 0.076 and 0.069, respectively, where R, = (Cw(lFoI - IFc1)2/CwF2)1/2 and R = CllFol - ~ F c ~ ~ /The ~ ~final F o atomic ~ . coordinates are given in Table I. One perspective view of the HFe3(CO)11- is shown in Figure 1. A crystal packing diagram with bonding viewed along the b axis is presented in Figure 2. Selected bond distances and angles are listed in Table 11. Tables of anistropic thermal parameters, coordinates of the hydrogen atoms, and observed and calculated structure factors are available; see the paragraph a t the end of the paper regarding supplementary material.
Results and Discussion Variations of the CO Frequencies of HFe3(CO)11with Its Environment. The bridging CO frequencies of the dialkylammonium salts of HFe3(CO)11-changed dramatically with the countercations and the solvents used. In the solid state, the absorption frequency of H2Et2N+ and H2(n-Bu)2N+salts appears a t an extremely low value of 1550 cm-I that is nearly 200 cm-' lower than its highest absorption frequency of 1745 cm-' in THF. The difference in the CO frequency change is believed to be the largest ever reported in the ion pairing studies of metal carbonylates. As the salts dissolve in chloroform or benzene, the bridging CO frequency increases to ca. 1650 cm-l from the value of 1550 cm-l in the solid state. The frequency further moves up to around 1740 cm-' in THF and in
Chen et al.
870 Organometallics, Vol. 6, No. 4, 1987 Table 11. Bond Distances (A)and Bond Angles (deg) of [H,(i-Pr),NI[HFe,(CO)111 Fe( 1)-Fe(2) Fe(l)-Fe(3) Fe(2)-Fe(3)
Fe3 Triangle 2.579 (2) Fe(2)-Fe(l)-Fe(3) 2.704 (3) Fe(l)-Fe(2)-Fe(3) 2.709 (3) Fe(l)-Fe(3)-Fe(2)
61.7 (1) 61.4 (1) 56.9 (1)
Carbonyl Groups Fe(l)-C(ll) Fe(l)-C(13) Fe(l)-C(14) C(ll)-O(ll) C( 13)-0( 13) C(14)-0(14) C(ll)-Fe(l)-C(l3) C(ll)-Fe(l)-C(l4) C(13)-Fe(l)-C(14) Fe(2)-C(21) Fe(2)-C(23) Fe(2)-C (24) c (21)-0(2 1) C(23)-0(23) C(24)-0(24) C(21)-Fe(2)-C(23) C(21)-Fe(2)-C(24) C(23)-Fe(2)-C(24) Fe(3)-C(31) Fe(3)-C(32) Fe(3)-C(33) Fe(3)-C (34) C (31)-0(31) C(32)-0(32) C(33)-0(33) C (34)-O(34) C(31)-Fe(3)-C(32) C(31)-Fe(3)-C(33) C(31)-Fe(3)-C(34) C(32)-Fe(3)-C(33) C(32)-Fe(3)-C(34) C(33)-Fe(3)-C(34) Fe(2)-C(12) Fe( 1)-C( 12) Fe(P)-HFe Fe( l)-HFe C(12)-0(12) Fe( l)-HFe-Fe(2) Fe(l)-C(12)-Fe(2) Fe(l)-C(12)-0(12) Fe(2)-C(12)-0(12) Fe( l)-HFe-C (12) Fe (2)-HFe-C (12)
Fe(l)-(COh 1.778 (16) Fe(2)-Fe(l)-C(11) 1.845 (14) Fe(Z)-Fe(l)-C(13) 1.755 (12) Fe(2)-Fe(l)-C(14) 1.175 (20) Fe(B)-Fe(l)-C(ll) 1.119 (17) Fe(3)-Fe(l)-C(13) 1.162 (16) Fe(3)-Fe(l)-C(14) Fe(l)-C(ll)-O(11) 92.9 (6) Fe(l)-C(13)-0(13) 97.7 (6) Fe(l)-C(14)-0(14) 97.8 (6)
112.7 (5) 117.7 (5) 130.4 (5) 164.7 (4) 102.3 (5) 78.6 (4) 173.7 (12) 172.9 (14) 173.5 (12)
Fe(2)-(COh 1.725 (13) Fe(l)-Fe(2)-C(21) 1.779 (13) Fe(l)-Fe(2)-C(23) 1.822 (12) Fe(l)-Fe(2)-C(24) 1.168 (17) Fe(3)-Fe(2)-C(21) 1.157 (17) Fe(3)-Fe(Z)-C(23) 1.139 (15) Fe(3)-Fe(2)-C(24) Fe(2)-C(21)-0(21) 95.9 (7) Fe(Z)-C(23)-0(23) 94.8 (6) Fe(2)-C(24)-0(24) 101.9 (6)
108.2 (5) 130.6 (4) 117.7 (5) 168.8 (5) 88.8 (5) 94.2 (4) 177.1 (11) 117.8 (12) 175.7 (12)
1.841 (12) 1.788 (16) 1.151 (16) 1.140 (17) 1.133 (14) 1.080 (21) 90.9 (7) 167.9 (7) 93.7 (7) 94.1 (6) 100.4 (7) 96.3 (6)
Bridging Groups 59.5 1.875 (10) C(12)-Fe(l)-HFe 1.957 (11) C(lZ)-Fe(Z)-HFe 60.8 1.652 C(12)-Fe( 1)-C( 11) 88.0 (6) 1.610 C(12)-Fe(l)-C(13) 162.0 1.211 (12) C(12)-Fe(l)-C(14) 99.9 (5) C(12)-Fe(2)-C(21) 90.5 (6) 104.4 C(12)-Fe(2)-C(23) 89.6 (5) 84.6 (4) C(12)-Fe(2)-C(24) 166.7 (6) 46.4 (3) 135.7 (9) Fe(2)-Fe(l)-C(12) 139.5 (10) Fe(3)-Fe(l)-C(12) 78.2 (3) 69.9 Fe( 1)-Fe(2)-C( 12) 49.1 (4) 65.7 Fe(3)-Fe(2)-C(12) 79.3 (4)
Counterion 1.542 (16) C(l)-N-C(4) 1.487 (16) C(2)-C(l)-C(3) 1.527 (18) C(B)-C(l)-N 1.534 (20) C(S)-C(l)-N 1.522 (26) C(5)-C(4)-C(6) 1.545 (26) C(5)-C4)-N C(6)-C(4)-N
N-*O(14)b
77.9 (5) 107.6 (5) 90.1 (5) 150.8 (5) 82.2 (5) 164.0 (5) 90.2 (5) 94.5 (5) 170.2 (15) 175.3 (11) 176.8 (13) 176.7 (15)
H Bonding 2.873 (11) 0(12)-HN(2)-N 3.110 (15) 0(14)*-HN(l)-N 1.932
117.4 (9) 112.7 (13) 107.8 (10) 106.1 (10) 113.7 (14) 109.0 (11) 108.3 (12) 171.6
166.8
L i
*,"
810
I 1 1
33
1800
1630
'OJ
,
COJ
cm
Crn
, s
, L
Y
Crn
Figure 3. The carbonyl absorption spectra of [H,(Et),N][HFe,(CO),J in the solid state and solutions.
L
.
l
l 1 8 L.
Crn
l
' hOL
ID
cm
'
Lb
I
"
cm
Figure 4. The carbonyl absorption spectra of HFe3(CO)''- with various cations in the solid state.
acetonitrile (Figure 3). On the other hand, the corresponding bridging CO frequency of the H2(i-Pr),N+salt appears a t 1650 cm-' in the solid state as shown in Figure 4, but one of the terminal CO absorptions occurs a t 1883 cm-'. This absorption is at least 20 cm-l lower in frequency than the lowest terminal CO absorption of the other HFe3(CO)11-salts presented in Figures 3 and 4. Interestingly, in benzene or chloroform, the bridging CO frequency remains a t approximately the same position as in the solid state, but the band at 1883 cm-l disappears. In THF, the bridging CO frequency shifts to 1745 cm-', the same position as that of the other HFe3(CO)1
